Function try_session_rc 

pub fn try_session_rc(
    stderr: &mut dyn Write,
) -> Result<Rc<RefCell<SessionHolder>>, ()>

Build SessionHolder from the environment. On failure (e.g. default γ Lima but limactl missing), writes to stderr and returns Err(()). Use DEVSHELL_VM=off or DEVSHELL_VM_BACKEND=host to force the host temp sandbox.